Congress, which thought it had cleaned its plate of budget cuts and other heavy fare before going on vacation a month ago, will return tomorrow to find the plate heaped high again.

The menu will be more varied, ranging from a huge farm bill, extension of civil rights and environmental legislation and major surgery on Social Security to matters such as the nomination of the first woman to the Supreme Court and the possible first expulsion of a senator since the Civil War. So-called "social issues" like abortion, mostly sidetracked so far, will also be pressing hard for consideration.

But the main entree is distressingly familiar: federal spending. There will be proposals for new and potentially more difficult spending cuts that may include the military as well as social welfare programs, coupled with an end-of-the-fiscal-year rush to keep money flowing into the government after current appropriations expire Sept. 30.

Congress left town on a political high in early August. Even those who despaired of the results could take pride in the fact that the two houses had moved legislative mountains in passing the biggest spending and tax cut bills in history, making a bigger impact in a few months than many congresses have done in a two-year lifetime.

But as members fanned out to lakes, mountains, foreign junkets and early-bird campaign forays for the 1982 elections, the euphoria dimmed. First there was bad news from financial markets, then upward revision of deficit estimates for the next three years and finally Reagan administration plans for another round of spending cuts aimed at keeping the deficits--and the markets--from getting out of hand.

Even without more spending cuts for the fiscal 1982 year that starts Oct. 1, Congress would be facing a groaning board of money bills, because its normal schedule for passing appropriations bills was disrupted by the push to pass the budget "reconciliation" program cuts demanded by President Reagan.

It also faces a Sept. 15 deadline for passage of a final budget resolution for 1982, although the deadline will surely be missed and few if any policy decisions are left to be made in the budget. There is little stomach for another round of "reconciliation" cuts in programs. The focus is now on controlling appropriations, or the actual money flow. The budget resolution is interesting mainly for what it will say about the anticipated deficit, which experts say is coming to look more like $60 billion than the $42.5 billion that the administration planned.

With the deadline for appropriations bills less than a month away, Congress has sent none of its 13 appropriations bills to Reagan for signature. Only one has gotten as far as a House-Senate conference. The House has passed five appropriations bills, and only two have been cleared by the Senate Appropriations Committee.

Just as last year, it appears likely that most, if not all, of the federal government will be financed by emergency stop-gap funding, a so-called "continuing resolution," as the new fiscal year begins next month.

But this continuing resolution could be much more than the routine kind of bridge loan that Congress provides when it misses deadlines. For one thing, some leaders, such as Senate Appropriations Committee Chairman Mark O. Hatfield (R-Ore.), want it to last a full 12 months rather than just the usual two or three months. Even more importantly, the Reagan administration is tempted to use it as a vehicle for perhaps as much as $15 billion in new savings.

The administration complains that money bills fashioned by the Democratic-controlled House will lead to real spending in fiscal 1982 that will exceed levels proposed by the President last March as well as, in some cases, targets set by Congress itself.

While legislative strategies have not yet been ironed out, the White House is seriously considering--and congressional leaders are bracing for--the possible veto of individual appropriations bills and even what might be called Gramm-Latta III.

Patterned after the successful administration budget cut substitutes that were sponsored earlier this summer by Reps. Phil Gramm (D-Tex.) and Delbert Latta (R-Ohio), an omnibus appropriations substitute would give the administration the framework for controlling the money that is actually spent. Once again it would be presenting the Reagan program in a form that Congress seems to like best: all in one package rather than in controversial pieces.

Continuing resolutions are usually pegged to existing levels or to House or Senate proposals for the next year, whichever is lower, with variations to account for particular needs and priorities. But there is nothing to prevent the administration from weighing in with substitute spending levels of its own, except, perhaps, the political risk of losing and ending the momentum of its almost unbroken winning streak in Congress.

Gramm-Latta II, which led to the $35 billion package of program cuts that Congress approved just before its summer recess, passed with only a few votes to spare and with some strategic concessions that the administration may have to back away from if it wants to keep a $42.5 billion deficit. Moreover, the August agony over interest rates and impending deficit levels raises the question of whether the Reagan economic program will be as popular in the autumn as it was in the spring.

Initial soundings in Congress last week indicate a mixed reaction, with some strategists advising against another go-for-broke effort. House Minority Leader Robert H. Michel (R-Ill.), for instance, was said by aides to be cool to the idea of a Gramm-Latta III. Another influential Republican lawmaker, looking to what may win over the markets, wants to see the administration concentrate on nailing down 1983 and 1984 cuts rather than nickel-and-diming down the 1982 deficit.

The likelihood of military cuts, or actually a scaling back of the huge spending increases recommended by the administration, is a new factor in the equation. Even some high-level Republicans say military restraint is critical to getting further domestic cutbacks, but a Senate GOP strategist predicts a "helluva fight," even within that chamber's Republican majority, over any major slashing of money for the Pentagon.

Thus there is a potential for some cracks in the solidarity of the GOP this fall, although continued preoccupation with the economy and budget may help keep abortion and other divisive social issues at bay for a while longer. Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) is understood to want to keep controversial social issues from impeding administration economic plans, but it is considered possible, for instance, that legislation that would in effect ban abortions could be attached as a rider to other legislation.

The once-scheduled early October adjournment now appears to be a distant dream. Among the other issues that could keep Congress in session until Thanksgiving or probably later are:

AWACs sale--The administration's major foreign policy battle of the year in Congress will formally get under way later this month when notification is filed of intent to sell Saudi Arabia $8.5 billion worth of defense equipment, including five Airborne Warning and Control Systems surveillance planes. Although a bare majority of members of both houses have signed statements opposing the sale, the administration is counting on the Republican-controlled Senate to let the sale proceed. It takes disapproval of both houses to block such a sale, which has never been done before.

Farm bill--Both houses are ready to go with separate versions of the huge farm bill, and the administration is pushing a less costly alternative to both that resembles, with a few exceptions reflecting political realities, its earlier proposals that were rejected by the agriculture committees of both houses. Senate action is expected first, possibly next week. Fierce battles are expected on many separate programs, including tobacco, peanuts and sugar. Time pressures are intense because the authorization for most major farm programs expires Sept. 30.

Clean Air and Water--The landmark Clean Air Act expires Sept. 30 and Congress is expected to give it routine extension until new provisions can be written, probably not until next year if major changes are to be made. Legislation is being drafted in the Senate, and the House plans to begin hearings later this month. Also pending are major revisions in the $2.4 billion sewage treatment grant program, with funding being withheld until changes are made.

Voting Rights--Enforcement provisions of the Voting Rights Act, passed in 1975 and twice extended, are up for renewal again next year, and the House is scheduled to take up its version of the measure in late September or early October. A key issue is bailout provisions for states, mainly Southern, that must get Justice Department approval for any changes in election laws. Senate action is not expected until next year.

Social Security--Faced with both short-term and long-range financing problems for the huge retirement system, the Senate Finance Committee is hoping to come up with a bill by early October, according to committee sources. A House Ways and Means subcommittee has also been working for some time on legislation. Among the issues are benefit formula changes, raising the retirement age for benefit purposes, reducing cost-of-living increases for pensions and the $122 per month minimum benefit that Congress repealed as of next February but apparently intends to revive in some modified form.

Supreme Court--Senate Judiciary Committee hearings for Sandra Day O'Connor are scheduled to begin this week, with confirmation by the Senate expected shortly thereafter.

Ethics--The Senate Ethics Committee has voted unanimously to expel Sen. Harrison A. Williams Jr. (D-N.J.) for "ethically repugnant" actions in connection with the FBI's Abscam operation aimed at ferreting out political corruption. But it urged no action until a federal judge rules on whether his jury conviction for bribery and conspiracy should be set aside because of due-process violations.

Debt ceiling--Sometime soon the debt ceiling will have to be raised up to or beyond the $1 trillion mark. The House slipped over the politically wrenching hurdle in connection with the budget, but the Senate still has to make the leap.

Crime--Democrats in both houses are pushing anti-crime legislation, apparently hoping to steal a march on the administration, which has said it plans to submit crime legislation later in the year.

Busing--Still pending before the Senate from before the recess is a filibuster over a Justice Department reauthorization rider that would prevent federal courts from ordering busing for school desegregation purposes. The Senate failed to end the filibuster by only one vote in July.

Abortion--A Senate Judiciary subcommittee proposal for legislation that could lead to the banning of abortions by defining life to begin at the moment of conception is being held up pending consideration of an anti-abortion constitutional amendment. Sen. Orrin G. Hatch (R-Utah), chairman of Judiciary's constitutional subcommittee, is championing a new version of an anti-abortion amendment that would, in effect, turn the issue over to the states.